Method of bending sintered material



M 26, 1960 R. w. BIGGS ,94 9

METHOD OF SENDING SINTERED MATERIAL Filed June 18, 1957 2 ShQetSP-Sheet1 VW mm mm, :1. 3 I. a l lllMunr NX m Om m INVENTOR. v ROBERT W 81665fibc/md WmQUZhE/n ATTORNEY July 2%, 1%0 R. w. BIGGS 2,946,369

METHOD OF SENDING SINTEREID MATERIAL Filed June 18, 1957 2 Sheets-Sheet2 INVENTOR.

ROBERT W B/GGS y m1 m1 5% midi-8mm ATTORNEY METHOD OF BENDING snvrnnnnMATERIAL Robert W. Biggs, Shaker Heights, Ohio, assignor to The S. K.Wellman Company, Bedford, Ohio, an Ohio corporation Filed June 18, 1957,Ser. No. 666,319 1 Claim. (Cl. 153-48) This invention relates to amethod of imparting a curved shape to an article.

Articles of the type referred to are produced by pressing or briquettingmetal powders with minor amounts of powders of one or more non-metallicingredients, such as graphite, and then heating the briquette to asintering temperature. In the past it was usually felt that such asintered briquette always had to be rather porous and of low tensilestrength, and that consequently it was necessary to provide areinforcing backing of a stronger metal, and this was acco'mplisheed byconducting the sintering step with the briquette held by pressureagainst a clean and properly prepared surface of a backing member as ofsteel. In the past, the necessity of pressing the powder to form thebriquette, and of bonding the briquette during or after sintering by theapplication of pressure, tended to limit the processes as a practicalmatter to the production of articles of flat configuration. For onething, it is difficult to briquette the powder to a curved shape andavoid uneven pressure and density, and subsequent cracking. On the otherhand, it is not diflicult to press in the flat. Bonding is also simplewhen the members are flat. Since it is frequently desirable to producelong, i.e. 13 long, contrasted with or A" thick, sintered metalliccontaining material articles of curved form, for example so they can beused for brake shoes adapted to engage a cylindrical or conical surface,it has been known to use a bending press and suitable dies. It has alsobeen known, as fully described and claimed in Tower and Lowey Patent2,446,891, issued August 10, 1948, to utilize a method of bending to apredetermined curvature by what might be termed roll-bending, comprisingthe steps of applying pressure to laterally extending areas of abi-metallic article successively and progressively along the length ofthe article, and controlling the amount of pressure (radial pressurethen being contemplated) so as to elongate more plastic facing to asufficiently greater extent than a less plastic backing member to bendthe article to the predetermined curvature and produce a curved articlehaving an outer more plastic face substantially free from cracks. In thecase of thick truck brake blocks of too large dimensions and/or toogreat a curvature to press directly, and too thick to roll bend, it hasalso been known, as disclosed and claimed in copending applicationSerial No. 390,178, now Patent No. 2,873,517, to make up an article byfirst flat compacting, and then cutting arcuate curves from the flatcompact, and then assembling the arcuate curves in flat side by flatside relation and then pressing in the direction of the curvature tobind them to each other and against a backing.

None of these prior art practices have been satisfactory for allapplications. Unbacked material can not be formed by any of the priormethods, for example -roll bending of a uni-metallic compact of pressedpowders without backing will lead to failure .to bend at all and with:the roll bending techniques applied to bi-metallic .articles one rollsometimes indents into the sintered or atent Q F 2,946,369 1 PatentedJuly 2 60 friction material to cause localized stretching throughoblique shear planes and subsequent cracking. And even if the materialsare not too thick to press to a curved shape, it is often too expensiveto provide the dies to do so. Making up -a flat compact first, and thencutting it into arcuate segments later assembled into side by siderelation is often found uneconomical, particularly in view of thepresent invention.

It is therefore an object of the present invention to provide animproved method by which sintered facing material articles, with orwithout a backing material, may be readily and rapidly bent, curved, orotherwise formed to desired curvature without injuring or cracking thefacing.

Other objects and advantages will become apparent and the invention maybe better understood from consideration of the following descriptiontaken in connection with the accompanying drawing, in which, by way ofexample:

Fig. 1 is a plan view of a flat bi-metallic blank to be bent to curvedshape;

Fig. 2 is a side elevation of the blank of Fig. 1;

Fig. 3 is a vertical section on line 3-3 of Fig. 2;

Fig. 4 is a diagrammatic plan view of a machine useful for forming theblank of Figs. 1-3;

Fig. 5 is a perspective view of a push bender useful for bendingsintered predominately metallic articles according to the invention.

Referring to Figs. :1-3, which, for clarity, are not to scale, I haveillustrated a fiat metallic blank 11 comprising a backing member 12 ofsolid metal such as steel, to which is integrally bonded a sinteredfacing 13 of originally powdered materials including at least one metal.The bi-metallic blank 11 may be to A thick by 2 wide by 13" long, thusmany times as long as it is thick, and may be formed in any suitablemanner, but I prefer to construct it in the manner described in WellmansUS. Patent No. 2,178,527, issued October 31, 1939. Generally speaking,the sintered facing 13 comprises a pressed and sintered mixture of oneor more metal powders to which minor amounts of one or more non-metallicsubstances are added. In connection with the present invention goodresults have been obtained using a two component mix of (by weight) ofiron powder and 15% of graphite, and good results .have also :beenobtained using a copper base mix comprising 7 1% copper, 8.5% iron, 5%tin, 1% lead, 5% silica, 4.5% graphite, and 5% molybdenum disulfide. Thepowdered mixture is pressed under a pressure of about eleven tons persquare inch to form a flat briquette, which may then .be clamped againsta clean and suitably prepared face of the metal backing member 12 andthe whole heated to a temperature of from 1200-1800 F. for a suflicientlength of time to sinter the metal powders together and to cause them tointegrally bond to the backing member.

Broadly speaking, the present invention relates to methods for rapidlyand smoothly bending either the flat blank shown in Figs. 13, or asintered material article without a backing, so that its facing will notcrack whether on the finally outer convex or inner concave surface ofthe member. The invention has its basis in .my discovery that by forcinglengthwise against a restraint, which places the neutral axis of bendingoutside the piece and away from the radius of bend and puts all thematerial in compression, such cracking can be avoided.

As one suitable means .of obtaining this all-over compression, I havediscovered that it is .possible to use a free-revolving roller and anopposed .curved die between which the blank is pushed. In Fig. 4 -l havediagrammatically illustrated apparatus of this type comprising a roller20 and a correspondingly curved pressure block die 21 between the two ofwhich the bimetallic blank is pushed. In this illustration the apparatusis provided with a hydraulic ram cylinder 22 having a piston 23actuating a piston rod 24, clevis block 25 and an ejector or pusher bar26 with the latter operating through. a .slot 27 in a main base plate 28to push thestock (such -as"11 of Fig. 1) between the roller 20, which isfree to revolve, and the pressure block 21. By sutably. selecting thediameter of the roller, the width of gap (to provide friction and/ orcompression restraint), and the pressure applied by the ejector, it ispossible to bend the bi-metallic blank to an accurate predeterminedcurvature in a very short period of time, and as successive fiat blanks11. are introduced in the slot, for example by hand one at a time witheach retraction of the pusher bar 26, arcuate shaped pieces are made tohop out of the machine as shown at 11, and when the run is finished itis an easy matter to remove the last piece 11 left in the machine byreleasing the radial pressure imposed by the die with respect to theroller.

If desired, slot 27 may be made adjustable widthwise to accommodatedifferent thickness of stock 11' as by providing a guide bar 29 madetransversely adjustable as it slides along pins 30 as determined by aspring biased bolt 31. The roller 20 and die 21 may also be changed toprovide a different size or radii of arcuate gap and some means (notshown) may be also provided for sliding guide bar 29 lengthwise so as toleave a minimum of unsupported space between it and the new roller 20.When different thicknesses of stock are to be run on a single machine,it is desirable to vary the pusher ejector width as by replacing part 26with another part of different size so that the ejector width willalways be about the same size as or slightly smaller than the stockbeing run.

Other suitable apparatus is shown in more detail in the perspective viewof Fig. in which like parts are like numbered as before and there isalso shown a handwheel 51 for advancing a screw 52 through a screw block53 which is fixed with respect to the main base 26. Ad-

Vance or retraction of the screw causes corresponding movement of a mainmounting plate 54 slidable with respect to a dovetail block 55 fixedwith respect to the base 28 and provided with a dovetail slot matingwith a dovetail 56 on the mounting plate 54.

Pressure block 21 is secured for back and forth movement with plate 54,as by the tabs 57, providing easy adjustability to provide differentpressures and, to some extent, to accommodate different size work. Thusthe hand wheel provides vennier adjustability to accommodate whateverthickness of stock might be desired to be run and, more importantly, toadjust the width of the arcuate gap with respect to original thicknessof stock in the fiat thereby to regulate the pressure imposed during thebending. To facilitate runs for stock of different size and/or to becurved to different radii the roller 20 is made removable to beinterchanged with one of a different size while the pressure block isalso arranged to be changeable.

Secured to rotate with screw 52 is a sprocket 58 for driving an endlesschain 59. Near the other end of the base 28, chain 59 drives a sprocket60 secured to rotate a screw 61' to advance or retract it through ascrew block 62 and thereby cause corresponding movement of base 54 andsupports including a front guide bar support 63 which in turn moves afront ejector support 64. An assembly of jointly movable parts includesplate 54, front and rear ejector supports 64, 7641', ejector 26, clevis25, rod 24, a cylinder support bracket 65, and cylinder 22, all movingwith respect to the main base 28.

Front and rear ejector supports 64, 641' may each be U-shaped to providea central clearance for passage of the clevis 25 (compare Fig. 4, whereejector and clevis and piston rod are full out, with Fig. 5, where theyare retracted) while at top and bottom the ejector supports are spacedapart to provide a clearance gap (preferably adjustable) to accommodatetop and bottom portions of the ejector pusher bar 26.

Near the middle of the machine the front guide bar support 63 may beconsidered bolted to drive a spacer 66 and a front guide bar 67, fiatstock 11 (if any) and rear guide bar 29 adjustably held in this case bybeing spring biased from a rear guide bar support 69 which is,preferably, adjustably secured with respect to sliding base plate 54.

In operation the operates the ejector responsive to introduction ofpressure through one or the other of hydraulic feed and exhaust conduits7273, and this causes compression and bending of any article in the dieand ejection of any article immediately previously therein. The slotclearance at the arc gap, where the piece 11" is shown in Fig. 4, isadjusted slightly smaller than the original thickness of the flat stock,particularly where sintered friction material or ultimate wear face isto be on the outside of the curvature, for otherwise the frictionmaterial might be stretched and crack. Machinery and process accordingto the invention will be operative to produce desirable pieces in asingle pass whereas with prior roll bender techniques it took manypasses.

I am not too positive as to the actual theory of operation, but it is myopinion that placing the material in initial lengthwise compression, asby forcing lengthwise against restraint on the sides and opposite end,permits, at the start of bending, placing the neutral axis of bendingoutside the sintered powdered material. and on the side opposite thebending fulcrum so that all the sintered material is in compression andcracking thereof is avoided. Where a solid metal backing is used, it isbelieved desirable but not necessary to have the steel backing incompression by placing the neutral axis of bending also outside of itand on the side opposite the fulcrum.

Particularly with a high graphite content of friction material it hasbeen found that prior roll bender techniques tended to crack thematerial and because of shear plane stresses render it useless.Processes according to the present invention prevent such cracking bykeeping all. material being processed in compression without any shearplanes, and there are further advantages over roll bending in that aproduct may be made without backing and final product may be formedright up to its end to a true radius all around without leaving a flaton either the leading or trailing end. In the case of bimetallicarticles (as already described and with solid metal backing and sinteredmaterial facing) shearing at the bond line is not likely to occur usingthe process of the invention regardless of whether the friction materialis to be ultimately on the inside or on the outside. For all the abovereasons there is achieved a new design freedom because any frictionmaterial mix can be used and in fact, solely friction material withoutany backing has been successfully processed according to thelongitudinal force bending method of the invention which puts theprocessed piece under compression without tension or stretching andwithout expensive'tooling.

There is thus provided a method of the type described capable of meetingthe object above set forth.

One aspect of the method of the invention is that all easily tearableparts of a piece to be formed are kept in compression. Compression isplaced on the piece even prior to the forming process and is kept oncritical portions of the piece during the forming. In other knownmethods, there are some regions not in compression so that shear andtensile forces may bring about fracture.

While I have illustrated and described particular embodiments, variousmodifications may obviously be made without departing from the truespirit and scope of the invention, which I intend to define in theappended claim. 1

I claim:

The method of bending a sintered compact of powdered materials arrangedin a fiat strip, which method References Cited in the file of thispatent UNITED STATES PATENTS Lignian June 10, 1941 Scully June 5, 1951Redmon June 12, 1956 FOREIGN PATENTS Great Britain Nov. 9, 1936 GreatBritain Feb. 6, 1952

